很多情况下我们需要多个线程互相协助，来完成同一个任务。但是线程很难从外部进行控制。利用线程同步技术可以使线程彼此交互，从而避免了外部控制对与时间和资源的浪费。-Many cases we need to assist each other to multiple threads in order to accomplish the same mission. But the thread is difficult to control from outside. The use of threa